$ { {3} \times \left[\begin{array}{r}{-1} \\ {4} \\ {4}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{3}\times{-1} \\ {3}\times{4} \\ {3}\times{4}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-3} \\ {12} \\ {12}\end{array}\right]}$